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What voltage does your panel generate? The combination of voltage and wattage will determine what you can charge.

A good rule of thumb is that you need at least 10-15% higher voltage out of your charger compared to what the battery normal produces. If your solar panel puts out a lower voltage than the battery, then it won't charge at all; instead you'd be driving current from the battery through the panel.

The wattage tells you basically how long it would take to charge your battery, but you need to do some "unit conversions" to figure it out.

I don't understand most of what kelseymh wrote and I'm guessing you don't either.In simple terms:A 43 watt panel on a solar tracker will put out up to 43 watts all day if it's sunny.If it's not on a tracker the panel will start producing a much lower amount just after sunup and the wattage will increase, peak at up to 43 watts at mid day, then decline till sundown.

The rating of 43 watts might be very misleading.I bought a commercial ebay type "20" watt panel that produced 27 volts and less than 3/4 of 1 amp.A system can only use 19 volts max so the panel really only put out about 12 watts of useable power.

if you haven't got a Multimeter you need to get one.Take your panel into the sun and measure the voltage and amperage.Multiply the volts by the amps to get the panels true wattage....usually much lower than you expect.

Your panel Has to put out between 15 and 19 volts to charge a 12 volt battery safely.A cheap controller is a great asset.You'll only need a little 6 amp one.It makes everything more simple and protects your battery from overcharging and being run too flat.

In my experience you could use a 50 amp hour battery but don't expect to be running too much from it.